A typical linear brushless motor of a rectangular configuration consists essentially of two parts: an armature assembly and a field assembly separated from each other by a small air gap.
An armature assembly, in turn, consists of a stack 10 of laminations with a three-phase winding positioned in its slots 12. Such a stack 10 is shown in FIG. 1. A field assembly is a rectangular soft magnetic plate with the rectangular magnets of alternating polarities facing the air gap.
Slot openings 14 for the armature assembly are normally selected to be as small as possible to minimize cogging forces. FIG. 2 shows typical slot openings 14. However, a small slot opening limits the size of the wire that can be used for the winding. In addition, any machine winding process becomes more difficult as the slot opening 14 gets smaller.
Additionally, in order to attach an armature assembly to a mechanical structure, the top surface 16 of the stack 10 should have drilled and tapped holes. Since laminations are not suitable for such holes, locking wedges 18 with mounting holes are provided, as shown in FIG. 1. Once the laminations are punched with the slots 20 for these locking wedges 18, the distance between locking wedges becomes fixed and cannot be changed without re-tooling the punch for the laminations.
U.S. patent application Ser. No. 10/116,495, filed Apr. 3, 2002, and assigned to the assignee of the present disclosure, addresses these disadvantages of prior armature assembly designs by providing an armature assembly design which facilitates winding of coils, while also minimizing cogging forces, and in which a mounting bracket structure is disclosed through which attachment to mechanical structures is simplified yet flexible.
There continues to be a need, however, for an armature design, which provides a reduction in detent forces caused by reluctance variations due to a finite length of the stack.